Such a method is known from NL-A-7805523, which discloses, amongst other things, that a catalyst suited to the polymerisation of olefins can be obtained by contacting a magnesium compound, which is obtained by reacting during one reaction step metallic magnesium with an organic halide RX, where R is an alkyl, alkenyl, aryl or cycloalkyl group containing from 1 to 20 carbon atoms, and X is a halogen, and an alkoxy group or aryloxy group-containing silane compound with a halogenized Ti-compound.